Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $245.89   5.825%   $260.2131   $260.21   $260.20   $260.20  
  Purchase #2 $189.43   6.299%   $201.3622   $201.36   $201.35   $201.40  
  Purchase #3 $130.26   8.497%   $141.3282   $141.33   $141.35   $141.30  
  Purchase #4 $89.67   4.105%   $93.351   $93.35   $93.35   $93.40  
  Purchase #5 $210.98   11.327%   $234.8777   $234.88   $234.90   $234.90  
  Purchase #6 $23.55   11.735%   $26.3136   $26.31   $26.30   $26.30  
  Purchase #7 $59.47   5.199%   $62.5618   $62.56   $62.55   $62.60  
  7 purchase totals = $949.25       $1,020.0076   $1,020.00   $1,020.00   $1,020.10